1. Field of the Invention
The present invention relates to a method of correction of a mask pattern which causes the mask pattern of a photomask used in the production of for example a semiconductor device to deform so as to give a transfer image close to a desired design pattern, a correction apparatus for executing that method of correction, a photomask obtained by that method of correction, a method of exposure performing exposure by using a photomask having that corrected mask pattern, a semiconductor device produced by performing photolithographic processing using a photomask having that corrected mask pattern, an apparatus for production of a photomask utilizing that method of correction, and an apparatus for production of a semiconductor device.
2. Description of the Related Art
In the production of a semiconductor device etc., the so-called photolithographic step of transferring a mask pattern of a photomask to a resist material on the semiconductor substrate by using light for exposure is indispensable.
In recent years, the miniaturization of the semiconductor devices to be prepared has been accompanied by an increasingly smaller design rule. Photolithographic processing approaching the limit of the theoretical resolution is now being carried out. For this reason, the resolution has become insufficient and there has arisen a problem of the disparity between the design mask pattern and the transferred resist pattern.
When such disparity occurs, problems such as deterioration of the performance of the device due to the deformation of the transfer pattern and a reduction of the manufacturing yield due to the bridging of the pattern (erroneous connection between parts of the pattern) and disconnection are induced.
Therefore, in the related art, to obtain a desired resist pattern, the mask pattern has been optimized by a trial and error procedure. For example, a plurality of modifying patterns are added to an individual design pattern based on experience, a transfer pattern is found by simulation from transfer experiments based on the mask pattern to which those modifying patterns were added, and the modifying pattern with which the transfer pattern closest to the design pattern is given is found by the trial and error system.
Further, recently, a method has been developed of automatically optimizing the mask pattern on a computer by correcting the optical proximity effect. In this system for correcting the optical proximity effect, a mask pattern which is deformed so that the transfer image is improved over the input design pattern is found by calculation.
However, these conventional technologies have the following problems.
In the conventional trial and error system, an enormous amount of time and number of steps are required for finding the optimum mask pattern, so this system can only be applied to restricted patterns. Accordingly, there was a problem that this system could not be applied to the correction of a mask pattern of a semiconductor device having an irregular pattern like an application-specific integrated circuit (ASIC).
Also, in the trial and error system, since the number of the mask patterns which can be evaluated is limited, there is a possibility that a better mask pattern might be overlooked and there was the problem that the precision of correction of the mask pattern was seriously limited.
For this reason, in recent years, technologies have been developed for automatically correcting mask patterns, but these already existing correction technologies have suffered from the following problems.
First, in the conventional automatic correction technology, no consideration is given to process margins such as margins of exposure or depth of focus, so there is a problem in that there sometimes occurs a case where the process margins such the margins of exposure and depth of focus are reduced. For this reason, there is a possibility that the manufacturing yield will rather be degraded by the automatic correction, so application of this to actual production processes has been difficult.
Also, in automatic correction, there is also proposed a method of finding the light intensity distribution by using simulation of the light intensity, using the contour lines sliced by the threshold value as the transfer image, and correcting the mask pattern so as to optimize this. In this method, however, the resist process is not considered, so the contour lines obtained by slicing the light intensity distribution do not coincide with the resist image obtained in the actual process and there is a problem that the resist image will not be sufficiently corrected even if correction is carried out.
Further, there is a problem that, in certain correction methods, distortion is generated in other portions by excessively correcting the corners of a pattern and the end portions of a line pattern, bridging of the resist pattern is caused when the amount of exposure or the focal position fluctuates, or a mask pattern which is difficult to fabricate is caused.